Always better to say what You did experienced yourself... All theories are good and work .........on the papers What I did is to put a black used water softner tank 13" X 54" holding about 17 gal. I strapped the tank to the basement's ceiling so the warmer place in the basement all year long. A simple valve syst can be add to ocasionaly inject some desinfection product if you are scare about bacteria.The cold water enters in this tank before the hot water tank as a pre-heating device. The next hydro bill went down. We must remember that, the most electric expensive appliance in a house after the heating ( supposing an electric heating system) is the hot water tank.And about legionella, the water should boil or be very close to to kill bacteria, so a good periodic hot water cleaning/flushing (a good flushing is more than just opening the hot water tank's drain valve) is the best way to prevent problems. And wash your hands once in a while

plumb-r wrote:He's right legionnaires disease loves sitting around in room temp. water.Especially , well water(no chlorine). Why not get a hot water maker and run it off the coal boiler? "Sting" That is great, I about busted a gut laughing. I don't no how many times I wish I could reach through the computer and cuff somebody.

.....amen to that plumbr ! I mean really.....what was coalkirk thinkin..???!

Almost posted earlier about getting a Indirect (hot water maker)...but, his question was about tempering water. And an indirect may add too much load for his boiler size and compromise his heat output on high heat load days.Another thought, mount a sizable tank higher than the boiler and allow it to be heated by thermosiphon, then per-heated water feeds into the electric HWH.This arrangement will avoid the sudden downward temp swing caused by 52* water entering the boiler during bigger demands...Mounted tank could be insulated...or not...your choice. Remember...Slow and steady wins the race!